1. Field of the Invention
The present invention relates to a frequency synthesizing apparatus for a multi-band radio frequency (RF) receiver, and more particularly, to a multi-frequency synthesizing apparatus and method which can reduce a circuit area and may be low powered.
2. Description of the Related Art
A high speed wireless data transceiving system such as a cellular phone, a digital multimedia broadcasting (DMB) phone, a personal digital assistant (PDA), etc., needs a frequency synthesizer or a frequency mixer processing multi-tones for frequency down conversion in a transceiver. For example, a multi-frequency synthesizer is utilized to receive an RF signal and convert the received RF signal into a baseband signal, in all bands utilizing a Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) scheme for a fourth generation mobile communication system or a ubiquitous system.
FIG. 1 is a diagram illustrating a multi-band of an OFDM scheme according to the related art. As shown in FIG. 1, five band groups #1, #2, #3, #4 and #5 are allowed to be allocated for an MB-OFDM scheme, i.e., between 3.1 and 10.6 GHz. The Federal Communications Commission (FCC) regulates that the band group #1 must be utilized, and other remaining band groups #2 to #5 may be utilized as necessary.
The fourth generation mobile communication system provides integrated services such as a voice, an image, multimedia, access to the Internet, a voice mail, an instance message, etc via one terminal with utilizing a satellite network, a wireless local area network (WLAN) and the Internet. As potential demands of the band group #1 for the fourth generation mobile communication increase, utilization of another band group is currently being discussed. Also, since a lot of interference from a WLAN utilizing an identical frequency band exists in a center frequency of the band group #2, i.e., in a 5544 MHz band, services of the fourth generation mobile communication utilizing a frequency band of the band group #3, #4 or #5 need to be developed.
FIG. 2 is a diagram illustrating a related art frequency synthesizer 200 for generating a multi-frequency signal. A predetermined receiver (Rx) mixer is utilized for an RF receiver to down convert a multi-band RF signal into a baseband. In this instance, a local signal RFO that is output from the frequency synthesizer 200 may be supplied to be synthesized with a received RF signal.
To obtain a multi-band local signal RFO, a single side band (SSB) mixer 230 is utilized. In this instance, the SSB mixer 230 generates a signal whose frequency is an addition of frequencies or a difference of frequencies between two received signals. However, in this case, the single SSB mixer 230 can only generate one of two components which are an addition of frequencies or a difference of frequencies between the two received signals. Accordingly, a plurality of SSB mixers and switches are generally utilized for down converting a large number of multi-band RF signals in a ubiquitous system.
The SSB mixers receive high frequency signals, RF1, RF2, . . . , from a voltage controlled oscillator (VCO)/frequency divider (DIV) 220, which is connected to a phase locked loop (PLL) 210, and synthesize a necessary frequency signal. In this instance, a plurality of PLLs, VCOs or DIVs may be utilized. Also, switches are needed for selecting any one of multi-frequency signals synthesized in the SSB mixers, which is necessary for down converting a received RF signal.
As described above, necessary multi-band signals may be generated by utilizing a large number of SSB mixers, PLLs, VCOs or DIVs. However, in this case, a required circuit area may be unacceptably increased to embody a PLL, a VCO/DIV and SSB mixers, and a huge amount of power may also be consumed. Also, since a large number of harmonics are generated that cause undesired tones, a stable and clean local signal LO may not be obtained.